Remove completed TODO for log rotation tests

Tests were added in fffe78eff669ebffa17f628974589f925ec6eb1d and 622864693af9343e860830dbbdee67bf688174be

TODO.txt

@@ -70,8 +70,6 @@
 
 - Expat error on Jens' system running slapd as root after reload.
 
-- Unit tests for log rotation.
-
 - Command-line arg tests.
 
 - Consider adding a dependency mechanism.  See pull request #20.